This project focuses on the characterization of the structural features of the cell membranes of thermophilic bacteria that permit these organisms to survive extremely high temperatures. We have isolated glycolipids from several thermophiles. FAB MS and GC-MS were used to characterize these molecules. We are now developing electrospray mass spectrometry (ESI-MS) as a more sensitive means for characterizing these lipids. The most striking feature of these molecules was the presence of very long chain fatty acyl groups (saturated, branched and unsaturated C30-C36). It is postulated that these long chain acyl groups modify membrane fluidity under high temperature conditions.